JP2009113426A - Liquid jetting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress unintended vibration of a driving element and a pressure chamber. <P>SOLUTION: The liquid jetting device includes a potential signal generating part which generates a potential signal, and the driving element which is deformed, when the potential signal is applied, in order to jet a liquid from a nozzle. The potential signal is expressed by a plurality of sine waves, its inclination varies continuously, and the potential signal applied to the driving element in a predetermined period when one liquid droplet is jetted from the nozzle includes a plurality of kinds of sine waves having a different period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid ejection apparatus.

  As a liquid ejecting apparatus, there is known an ink jet printer that ejects ink by driving a driving element (piezo element) by a driving signal, causing a pressure change in a pressure chamber filled with ink by deformation of the driving element.

Among them, an ink jet printer using a drive signal composed of trapezoidal waves has been proposed. In such a printer, for example, the pressure chamber is expanded by linearly increasing the potential from the intermediate potential to the maximum potential, and the potential is contracted from the maximum potential to the minimum potential at a stretch after a predetermined period. To eject ink. (For example, see Patent Document 1)
JP-A-5-69542

  However, the trapezoidal wave drive signal described in Patent Document 1 has a point where the amount of change in potential with respect to a predetermined period changes suddenly (for example, a point where the potential rising portion switches to the potential holding portion). There is a possibility that unintended vibration (deformation) may occur in the drive element and the pressure chamber at such a point where the amount of potential change suddenly changes.

  Therefore, an object is to suppress unintended vibrations of the drive element and the pressure chamber.

  A main invention for solving the above-described problems includes a potential signal generation unit that generates a potential signal, and a drive element that is deformed when a potential signal is applied in order to eject liquid from a nozzle, and the potential The signal is represented by a plurality of sine waves, and the inclination continuously changes, and the potential signal applied to the drive element during a predetermined period in which one liquid droplet is ejected from the nozzle has a different period. A liquid ejecting apparatus comprising a plurality of types of sine waves.

  Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

=== Summary of disclosure ===
At least the following will become apparent from the description of the present specification and the accompanying drawings.

That is, a potential signal generation unit that generates a potential signal and a drive element that is deformed when a potential signal is applied in order to eject liquid from a nozzle, and the potential signal is represented by a plurality of sine waves. In addition, the potential signal applied to the driving element during a predetermined period in which one of the liquid droplets is ejected from the nozzle is composed of a plurality of types of sine waves having different periods. A liquid ejection apparatus characterized by the above is realized.
According to such a liquid ejecting apparatus, since the potential is smoothly changed, it is possible to suppress the occurrence of unintentional vibration in the periphery of the driving element (pressure chamber). In addition, a potential signal suitable for the purpose can be applied to the driving element.

This liquid ejection apparatus has a pressure chamber that communicates with the nozzle and is expanded and contracted by deformation of the drive element, and the period of at least one of the sine waves is the natural vibration period Tc in the pressure chamber. Equality.
According to such a liquid ejecting apparatus, the vibration (expansion / contraction) of the pressure chamber caused by the natural vibration period Tc and the vibration of the pressure chamber caused by the drive signal can be synchronized, so that the pressure chamber can be vibrated efficiently. it can.

In this liquid discharge apparatus, the period of the sine wave of the potential signal applied to the drive element when liquid is discharged from the nozzle is equal to the natural vibration period Tc in the pressure chamber.
According to such a liquid ejecting apparatus, the vibration of the pressure chamber due to the natural vibration period Tc and the vibration of the pressure chamber due to the drive signal are synchronized, and the pressure chamber can be expanded and contracted more greatly, so that the ejection efficiency is increased. As a result, a large amount of liquid can be discharged. In other words, the liquid can be discharged with a small potential.

In this liquid ejection apparatus, the amplitude of the potential signal is A, the angular frequency of the potential signal is ω, the initial phase of the potential signal is φ, and the vibration center adjustment value of the potential signal is B. In this case, the expression representing the drive potential V (t), which is the potential indicated by the potential signal at time t, is V (t) = A × sin (ωt + φ) + B.
According to such a liquid ejecting apparatus, a potential signal that is represented by a sine wave and whose slope continuously changes can be obtained. A potential signal having a desired shape can be obtained by changing each parameter.

In this liquid ejection apparatus, the amplitude of the potential signal is A, the attenuation term of the potential signal is exp (−γt), the angular frequency of the potential signal is ω, and the initial phase of the potential signal is φ When the vibration center adjustment value of the potential signal is B, the expression representing the drive potential V (t), which is the potential indicated by the potential signal at time t, is V (t) = A × exp (−γt) Xsin (ωt + φ) + B.
According to such a liquid ejecting apparatus, a potential signal that is represented by a sine wave and whose slope continuously changes can be obtained. A potential signal having a desired shape can be obtained by changing each parameter.

This liquid ejection apparatus has a pressure chamber that communicates with the nozzle and expands and contracts by deformation of the drive element, and the potential signal is obtained from the first sine wave and the first sine wave. A second sine wave having a long cycle, and the first sine wave deforms the drive element, and the deformation causes the pressure chamber communicated with the nozzle to expand and contract from the nozzle. It is a waveform for discharging a liquid, and the second sine wave is a waveform for expanding the contracted pressure chamber and suppressing vibration in the pressure chamber.
According to such a liquid ejecting apparatus, the liquid can be ejected with a stronger force by deforming the pressure chamber in a relatively short period. Further, by expanding the pressure chambers over a relatively long period of time, vibration suppression effects can be obtained for all the pressure chambers regardless of variations in vibrations caused by the pressure chambers.

In this liquid ejecting apparatus, the amplitude of the first sine wave is larger than the amplitude of the second sine wave.
According to such a liquid ejecting apparatus, it is possible to eject liquid with a greater force, and it is possible to eject a large amount of liquid.

This liquid ejection apparatus has a pressure chamber that communicates with the nozzle and expands and contracts by deformation of the drive element, and the potential signal is obtained from the first sine wave and the first sine wave. A second sine wave having a shorter period and a third sine wave having a longer period than the first sine wave, the first sine wave deforms the driving element, and The second sine wave is for deforming the driving element, and contracting the pressure chamber by the deformation to discharge liquid from the nozzle. The waveform is a waveform, and the third sine wave is a waveform for inflating the contracted pressure chamber to control vibration in the pressure chamber.
According to such a liquid ejection device, air can be prevented from entering the pressure chamber during expansion, and the pressure chamber can be deformed in a relatively short period of time to eject liquid with a stronger force. You can do it. Further, by expanding the pressure chambers over a relatively long period of time, vibration suppression effects can be obtained for all the pressure chambers regardless of variations in vibrations caused by the pressure chambers.

In this liquid discharge apparatus, the amplitude of the first sine wave is larger than the amplitude of the third sine wave, and the amplitude of the second sine wave is larger than the amplitude of the third sine wave. Big thing.
According to such a liquid ejecting apparatus, the pressure chamber can be expanded and contracted with a larger force, so that a large amount of liquid can be ejected.

In such a liquid ejecting apparatus, at a point where one sine wave is switched to another sine wave having a different period, a potential indicated by one sine wave is equal to a potential indicated by another sine wave, and the sine wave is The slope of the expression that represents is equal to the slope of the expression that represents another sine wave.
According to such a liquid ejecting apparatus, it is possible to obtain a potential signal that is represented by a sine wave and whose inclination changes continuously.

In such a liquid ejecting apparatus, at the switching point, the slope of the formula representing a certain sine wave and the slope of the formula representing another sine wave are zero.
According to such a liquid ejecting apparatus, even if an error occurs at the switching point, the potential difference can be minimized.

In such a liquid ejecting apparatus, the switching point does not exist during a period in which the liquid is ejected from the nozzle.
According to such a liquid ejecting apparatus, a predetermined amount of liquid can be ejected.

In this liquid ejection apparatus, the potential signal has a waveform obtained by adding two sine waves having different formulas.
According to such a liquid ejection apparatus, a potential signal having a desired shape can be obtained.

In this liquid ejection apparatus, the potential signal includes a first sine wave and a second sine wave having an amplitude smaller than that of the first sine wave, and the second sine wave is The potential value becomes negative during a period in which the pressure chamber expands from a period in which the pressure chamber communicating with the nozzle contracts.
According to such a liquid ejecting apparatus, the potential signal can increase the maximum potential and decrease the minimum potential as compared with the first sine wave. Therefore, the liquid can be discharged with a larger potential difference, and a large amount of liquid can be discharged.

=== Configuration of Inkjet Printer ===
Hereinafter, an embodiment will be described by taking a liquid ejecting apparatus as an ink jet printer and taking a serial printer (printer 1) in the ink jet printer as an example.

  FIG. 1 is a block diagram showing the overall configuration of the printer 1 according to this embodiment. 2A is a perspective view of the printer 1, and FIG. 2B is a cross-sectional view of the printer 1. The printer 1 that has received print data from the computer 60 that is an external device controls each unit (conveyance unit 20, carriage unit 30, head unit 40) by the controller 10, and forms an image on the sheet S (medium). Further, the detector group 50 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result.

  The controller 10 is a control unit for controlling the printer 1. The interface unit 11 is for transmitting and receiving data between the computer 60 as an external device and the printer 1. The CPU 12 is an arithmetic processing unit for controlling the entire printer 1. The memory 13 is for securing an area for storing the program of the CPU 12 and a work area. The CPU 12 controls each unit by the unit control circuit 14.

  The transport unit 20 is for transporting the paper S by a predetermined transport amount in the transport direction during printing after the paper S is sent to a printable position, and includes a paper feed roller 21, a transport motor 22, and a transport A roller 23, a platen 24, and a paper discharge roller 25 are included. The paper feed roller 21 is rotated, and the paper S to be printed is sent to the transport roller 23. When the paper detection sensor 51 detects the position of the leading edge of the paper S sent from the paper supply roller 21, the controller 10 rotates the transport roller 23 to position the paper S at the print start position. When the paper S is positioned at the print start position, at least some of the nozzles of the head 41 face the paper S.

  The carriage unit 30 is for moving the head 41 in a direction intersecting the transport direction (hereinafter referred to as a movement direction), and includes a carriage 31 and a carriage motor 32.

  The head unit 40 is for ejecting ink onto the paper S, and has a head 41 and a head drive circuit 42 for driving the head 41. A plurality of nozzles, which are ink discharge portions, are provided on the lower surface of the head 41. Each nozzle has a pressure chamber containing ink, and a drive element (piezo element) for changing the volume of the pressure chamber to discharge ink. ) Is provided.

  The serial printer 1 alternately performs a dot forming process in which ink is intermittently ejected from the head 41 moving in the movement direction to form dots on the paper S and a conveyance process in which the paper S is conveyed in the conveyance direction. By repeating the above, dots are formed at positions different from the positions of the dots formed by the previous dot formation process, and the image is completed.

=== About driving of the head ===
3A is a diagram illustrating the drive signal generation circuit 70, and FIG. 3B is a diagram illustrating generation of the potential waveform signal COM ′. FIG. 4 is a diagram showing the drive signal generation circuit 70 and the head drive circuit 42, and shows that the piezo elements corresponding to the respective nozzles are operated by the head drive circuit 42. FIG. 5 is a timing chart of each signal.

<About drive signal generation circuit>
As shown in FIG. 3A, the drive signal generation circuit 70 includes a waveform generation circuit 71 and a current amplification circuit 72, and generates a drive signal COM that is used in common for a certain nozzle group.

  First, the controller 10 sequentially outputs a DAC value (digital signal waveform information) to the waveform generation circuit 71 every update period τ. Then, the waveform generation circuit 71 generates a potential waveform signal COM ′ (analog signal waveform information) that is the basis of the drive signal COM based on the DAC value. That is, the waveform generation circuit 71 corresponds to a conversion circuit that converts digital data into analog data (potential signal).

  As shown in FIG. 3B, the controller 10 outputs a DAC value corresponding to the potential V1 at the timing t (n) defined by the clock signal CLK. Thereby, the output from the waveform generation circuit 71 rises from the potential V0 to the potential V1 during the period τ (n). Then, from the period τ (n) to the period τ (n + 4), the output from the waveform generation circuit 71 rises from the potential V1 to the potential V2. Further, after the timing t (n + 5), the controller 10 inputs a DAC value corresponding to the potential V 3 to the waveform generation circuit 71. As a result, the output of the waveform generation circuit 71 falls from the potential V2 to the potential V3 in the cycle τ (n + 5), and then the potential gradually falls. As described above, the potential output from the waveform generation circuit 71 rises and falls according to the DAC value input from the controller 10. The DAC values sequentially input from the controller 10 are sequentially output from the waveform generation circuit 71 as the potential waveform signal COM ′. The DAC value is stored in the memory 13 as a potential change amount corresponding to each timing t (n). Information in the memory 13 is read by the controller 10 and output to the waveform generation circuit 71. Further, the present invention is not limited to this, and information relating to a waveform expression representing a drive signal (eg, V (t) = A × exp (−γt) × sin (ωt + φ) + B) is stored in the memory 13, and the controller 10 relates to the waveform expression. The potential change amount corresponding to each timing may be calculated from the information and output to the waveform generation circuit 71 as a DAC value.

  Next, the current amplification circuit 72 amplifies the current of the potential waveform signal COM ′ and outputs it as a drive signal COM. The current amplifier circuit 72 includes a rising transistor Q1 (NPN type transistor) that operates when the potential of the drive signal COM rises, and a falling transistor Q2 (PNP type transistor) that operates when the potential of the drive signal COM decreases. The raising transistor Q1 has a collector connected to the power supply and an emitter connected to the output signal line of the drive signal COM. The descending transistor Q2 has a collector connected to the ground (earth) and an emitter connected to the output signal line of the drive signal COM.

  When the raising transistor Q1 is turned on by the potential waveform signal COM ′ from the waveform generation circuit 71, the drive signal COM rises and the piezo element PZT is charged. On the other hand, when the lowering transistor Q2 is turned on by the potential waveform signal COM ', the driving signal COM is lowered and the piezo element PZT is discharged.

<About the head drive circuit>
The head drive circuit 42 includes 180 first shift registers 421, 180 second shift registers 422, a latch circuit group 423, a data selector 424, and 180 switches SW. The head drive circuit 42 corresponds to a nozzle group composed of 180 nozzles, and the numbers in parentheses in the figure indicate the numbers of the nozzles to which the members (or signals) correspond.

  First, the print signal PRT is input to the 180 first shift registers 421 and then input to the 180 second shift registers 422. As a result, the serially transmitted print signal PRT is converted into 180 2-bit print signals PRT (i). The print signal PRT (i) is a signal corresponding to the data of one pixel assigned to the nozzle #i.

When the rising pulse of the latch signal LAT is input to the latch circuit group 423, 360 data of each shift register is latched in the latch circuit group 423. When the rising pulse of the latch signal LAT is input to the latch circuit group 423, the rising pulse of the latch signal LAT is also input to the data selector 424, and the data selector 424 is in the initial state.
Further, the data selector 424 selects a 2-bit print signal PRT (i) corresponding to each nozzle #i from the latch circuit group 423 before latching (before the initial state), and each print signal PRT (i). The switch control signal prt (i) corresponding to is output to each switch SW (i).

  On / off control of the switch SW (i) corresponding to the piezo element PZT (i) is performed by the switch control signal prt (i). Then, the on / off operation of the switch applies or blocks the drive signal COM transmitted from the drive signal generation circuit 70 to the piezo element (DRV (i)), and ink is ejected from the nozzle #i or ejected. Not. That is, a necessary portion in the drive signal COM is selectively applied to the piezo element.

<Ink ejection>
For example, when the level of the switch control signal prt (i) is “1”, the switch SW (i) is turned on, and the drive waveform W (sinusoidal signal) within the repetition period T, which the drive signal COM has, remains as it is. The drive waveform W is applied to the piezo element PZT (i). When the drive waveform W is applied to the piezo element PZT (i), the piezo element PZT (i) is deformed according to the drive waveform W, and the elastic film (side wall) that partitions a part of the ink chamber is deformed. Then, a predetermined amount of ink in the ink chamber is ejected from the nozzle #i. On the other hand, when the level of the switch control signal prt (i) is “0”, the switch SW (i) is turned off, and the drive waveform W included in the drive signal COM is cut off.

  The print signal prt (i) for one pixel is 1-bit data, and one pixel is expressed by two gradations of “a dot is formed” and “a dot is not formed”. In this case, as shown in FIG. 5, when the switch control signal prt (i) is “1”, the drive waveform W is applied to the piezo element PZT (i), and a predetermined amount of ink is ejected from the nozzle #i. , Dots are formed. When the switch control signal prt (i) is “0”, the drive waveform W is not applied to the piezo element PZT (i), so that the piezo element PZT (i) is not deformed, and no dot is formed.

=== Generation of Free Vibration by Drive Signal COM ===
First, the configuration around the pressure chamber will be described in detail.
6A is a cross-sectional view of the main body of the head 41, and FIG. 6B is a cross-sectional view showing an enlarged main part of the head main body 41. The main body of the head 41 includes a case 411, a flow path unit 412, and a piezo element unit 413. The case 411 is a block-shaped member formed inside the storage chamber 411 a for storing the flow path unit 412. The channel unit 412 includes a channel forming plate 412a, an elastic plate 412b bonded to one surface of the channel forming plate 412a, and a nozzle plate 412c bonded to the other surface of the channel forming plate 412a. . The flow path forming plate 412a is formed with a groove portion serving as a pressure chamber 412d, a through hole serving as a nozzle communication port 412e, a through port serving as a common ink chamber 412f, and a groove portion serving as an ink supply path 412g. The elastic plate 412b has a support frame 412h and an island portion 412j to which the tip of the piezo element PZT is joined. An elastic region is formed by the elastic film 412i around the island portion 412j.

  The piezo element unit 413 includes a piezo element group 413a, an adhesive substrate 413b, and an element wiring substrate 413c. The piezo element group has a comb-teeth shape, and each comb-teeth portion corresponds to the piezo element PZT. The piezo element group 413a includes a number of piezo elements PZT corresponding to the nozzles Nz. As shown in FIG. 4, a drive signal COM is applied in parallel to each piezo element PZT. The bonding substrate 413b is a rectangular plate, and the piezoelectric element group 413a is bonded to one surface and the other surface is bonded to the case 411. The element wiring board 413c is a wiring material for applying a drive signal COM to each piezo element PZT. A head drive circuit 42 is mounted on the element wiring board 413c.

  The piezo element PZT is deformed by applying a potential difference between opposing electrodes. In this example, it expands and contracts in the longitudinal direction of the element. The amount of expansion / contraction is determined according to the potential of the piezo element PZT. The potential of the piezo element PZT is determined by the application portion in the drive signal COM. Accordingly, the piezo element PZT expands and contracts according to the potential applied by the application portion of the drive signal COM. When the piezo element PZT expands and contracts, the island portion 412j is pushed toward the pressure chamber 412d or pulled in the opposite direction. At this time, since the elastic film 412i around the island portion is deformed, ink can be efficiently discharged from the nozzle Nz. Such a piezo element PZT is an element that is charged and discharged by the drive signal COM, and corresponds to an element that performs an operation for ejecting ink. When the piezo element PZT is used for the main body of the head 41, the amount and speed of the ejected ink are controlled variously according to the applied driving waveform, or the meniscus (the nozzle Nz is exposed without ejecting the ink). The free surface of the ink can be vibrated.

FIG. 7 is an equivalent circuit of the vibration generating portion of the head 41. As described above, when the drive signal COM is applied to the piezo element PZT corresponding to each nozzle to deform the drive element and the pressure chamber (forced vibration), vibration (free vibration) is generated in the drive element and the pressure chamber. FIG. 7 is a circuit showing this free vibration, and the symbols in the figure are as follows.
Ma: Inertance in piezo element (medium mass per unit length, kg / m ⁴ )
Mn: Inertance at nozzle opening Ms: Inertance at ink supply section Rn: Resistance at nozzle opening (internal loss of medium, N · s / m ⁵ )
Rs: resistance in the ink supply unit Cc: compliance in the pressure chamber (volume change per unit pressure, m ⁵ / N)
Ca: Compliance in the piezo element Cn: Compliance in the nozzle opening P: Drive waveform (potential signal) applied to the piezo element is converted into an equivalent pressure

From the equivalent circuit, the natural vibration period Ta of the piezoelectric element system is expressed by the following equation.
Ta = 2π√ (Ma · Ca)
Similarly, the natural vibration period Tc in the pressure chamber is expressed by the following equation.
Tc = 2π√ [(Mn · Ms · Cc) / (Mn + Ms)]
Similarly, the natural vibration period Tm of the meniscus is expressed by the following equation.
Tm = 2π√ [(Mn + Ms) Cn]
=== About the Drive Signal COM ===
<Drive signal of comparative example>
FIG. 8 is a diagram illustrating the drive signal COM ′ of the comparative example. First, as a comparative example of drive signals used in the present embodiment, a relationship between a trapezoidal wave drive signal COM ′ and ink ejection will be described.

The drive signal generation circuit 70 outputs the intermediate potential Vc until time T0, and the intermediate potential Vc is applied to the piezo element. The volume of the pressure chamber at this time is set as a reference volume. Thereafter, between time T0 and time T1, the drive signal generation circuit 70 increases the potential from the intermediate potential Vc to the maximum potential Vh. Due to this potential increase, the piezo element PZT contracts in the longitudinal direction and expands the volume of the pressure chamber. As a result, the pressure in the pressure chamber is reduced.
Then, after maintaining the maximum potential Vh until time T2, the drive signal generation circuit 70 decreases the potential from the maximum potential Vh to the minimum potential Vl between time T2 and time T3, and expands the piezoelectric element. As a result, the volume of the pressure chamber shrinks, the pressure in the pressure chamber is increased at once, and ink is ejected from the nozzle Nz.
Finally, the drive signal generation circuit 70 maintains the lowest potential Vl until time T4, and increases the potential from the lowest potential Vl to the intermediate potential Vc between time T4 and time T5. As a result, the volume of the contracted pressure chamber expands, and the volume in the pressure chamber is returned to the reference volume.

  Further, in the meniscus that vibrates after ink ejection, the driving signal is set to rise from the lowest potential Vl to the intermediate potential Vc when the meniscus is most drawn to the pressure chamber side and turns to the nozzle opening side. Then, due to the expansion of the pressure chamber, the meniscus that tries to turn to the nozzle opening is pulled back to the pressure chamber side, so that the meniscus decreases the kinetic energy and the meniscus vibration is attenuated. That is, it is preferable to adjust the potential holding period from time T3 to time T4 so that the pressure chamber is expanded at the timing when the meniscus vibration is attenuated.

As shown in FIG. 8, the trapezoidal wave drive signal COM ′, which is a comparative example, has a bent portion (eg, times T1, T3, etc.). A bent portion is a portion where the amount of change in potential (gradient of potential change) with respect to a predetermined period changes. For example, while the potential increases linearly from time T0 to time T1, the increase in potential stops at time T1, and the potential is kept constant. At time T1, the volume in the pressure chamber reaches the volume corresponding to the maximum potential Vh, so that the increase in the potential of the drive signal COM ′ is stopped and the contraction of the piezoelectric element is stopped so that the pressure chamber does not expand further. . However, even if the increase in the potential of the drive signal COM ′ is stopped, the piezo element and the pressure chamber cannot suddenly stop contracting or expanding due to the action of inertia. As a result, unintended vibration (deformation) occurs in the piezo element and the pressure chamber (hereinafter, the piezo element and the pressure chamber are collectively referred to as an ink discharge unit).
In other words, the trapezoidal drive signal COM ′ includes a high frequency component, and unintentional vibration is generated in the piezoelectric element and the pressure chamber due to the influence of the high frequency component.

  If unintentional vibration occurs in the ink ejection section, a predetermined amount of ink is not ejected from the nozzle, and image degradation occurs. In addition, in order to prevent the meniscus from drying, there is a possibility that the ink may be ejected although a drive signal that does not eject ink is applied (microvibration). That is, it can be said that there is a limit to the response of the ink ejection unit to the trapezoidal wave drive signal COM '.

  Therefore, it is an object of the present embodiment to suppress the occurrence of unintended vibrations in the ink ejection unit (piezo element or pressure chamber). Hereinafter, the drive signal COM used in the present embodiment will be described.

<Example 1: First drive signal COM1>
FIG. 9A is a diagram illustrating the first drive signal COM1 according to the first embodiment. The horizontal axis represents the time change, and the vertical axis represents the driving potential V (t) [V] at time t. The first drive signal COM1 is not a trapezoidal drive signal COM ′, but is represented by a sine wave as shown in the figure, and the slope continuously changes. The drive potential before time t0 is the intermediate potential Vc, and the volume of the pressure chamber at this time is the reference volume. From time t0 to time t1, the potential applied to the piezo element increases (intermediate potential Vc → maximum potential Vh), so that the piezo element contracts and the pressure chamber expands more than the reference volume (the pressure in the pressure chamber increases). Depressurize). From time t1 to time t2, the potential applied to the piezo element decreases (maximum potential Vh → lowest potential Vl), the piezo element expands, and the pressure chamber contracts (the pressure in the pressure chamber is increased). Ink droplets are ejected from the nozzles. Finally, from time t2 to time t3, the potential applied to the piezo element rises (lowest potential Vl → intermediate potential Vc), whereby the contracted pressure chamber expands, and the volume in the pressure chamber is returned to the reference volume. .

  Unlike the trapezoidal wave drive signal COM ′, such a sine wave drive signal COM does not have a portion that bends during one ink droplet ejection period (from time t0 to time t3), and changes in potential. It is smooth. Therefore, it is possible to prevent unintended vibrations from occurring in the piezoelectric element and the pressure chamber.

  In other words, such a sinusoidal drive signal COM does not contain a high-frequency component like the trapezoidal drive signal COM ′, so that unintentional vibrations are prevented from occurring in the piezoelectric element and the pressure chamber. it can.

  More specifically, in the first drive signal COM1, the potential increase rate becomes smaller as it approaches the time t1, which is a point where the change in the drive potential V (t) switches from increase to decrease. In addition, the potential increase rate is small in the vicinity of time t1. Therefore, even if the potential increase is stopped at time t1 and the potential starts to decrease immediately after time t1, the piezoelectric element is contracted and the pressure chamber is expanded immediately after time t1, contrary to the drive signal COM1. It is prevented that the inertial force to work. Therefore, it is possible to suppress unintended vibration (deformation) from occurring in the piezoelectric element and the pressure chamber.

  Similarly, as the change in the driving potential V (t) approaches time t2, which is a point where the change from decrease to increase, the potential decrease rate decreases. For this reason, even if the potential decrease stops at time t2 and the potential starts to increase immediately after time t2, inertial force (force to expand and contract) acts on the piezoelectric element and the pressure chamber. It is prevented. Therefore, it is possible to prevent unintended vibration (deformation) from occurring in the piezoelectric element and the pressure chamber.

  Further, the piezo element begins to gradually expand from time t1, and the expansion rate (the amount of expansion for a predetermined period) becomes maximum at an intermediate point between time t1 and time t2, and then gradually decreases as time approaches time t2. Become. Therefore, the pressure chamber also begins to gradually contract from time t1, and the contraction rate becomes the largest at an intermediate point between time t1 and time t2, and then gradually decreases as it approaches time t2. In other words, in the ink droplet ejection period from time t1 to time t2, the piezoelectric element and the pressure chamber gradually start to be deformed and gradually deformed so that the piezoelectric element and the pressure chamber are transformed. The occurrence of unintended vibration is suppressed, and as a result, a predetermined amount of ink is ejected.

  In addition, since vibrations of general structures such as ink ejection portions (piezo elements and pressure chambers) are generated in a sine wave shape, it is preferable to use a sine wave drive signal COM rather than a trapezoidal wave drive signal COM ′. It can be said that the deformation (vibration) of the discharge part becomes natural and unintentional vibration hardly occurs.

  In this way, by suppressing the occurrence of unintended vibrations in the ink discharge portion, it is possible to discharge a predetermined amount of ink, and ink may be accidentally discharged even during slight vibration. Disappear. That is, by using the sine wave drive signal COM, the ink ejecting unit always performs a desired movement (for example, ejecting a predetermined amount of ink), so that the print image can be prevented from deteriorating. In addition, in order to discharge ink against unintended vibrations, for example, it is not necessary to increase the potential of the drive signal, so that it can be said that energy loss is prevented.

  Further, in the present embodiment, the drive signal generation circuit 70 (corresponding to a conversion circuit) DA converts the DAC value (digital data) from the controller 10 into a drive signal COM (potential signal) corresponding to the DAC value. The controller 10 outputs a DAC value to the drive signal generation circuit 70 so that the drive signal COM becomes a sine wave. For example, a sinusoidal drive signal can also be generated by an LC circuit or the like, but the cycle of the drive signal is fixed in the LC circuit. Therefore, the degree of freedom in designing the drive signal COM increases when the drive signal COM is generated by the DA conversion circuit (drive signal generation circuit 70).

  Incidentally, the first drive signal COM1 is composed of a first waveform W1 (first sine wave) having a relatively short cycle and a second waveform W2 (second sine wave) having a relatively long cycle, and the time t2 The type of the drive waveform W is switched at. When such a first drive signal COM1 is generated, if the DA conversion circuit (drive signal generation circuit 70) is used, the DAC value output from the controller 10 at time t2 can be changed only from the first waveform W1. Two waveforms W2 can be switched. That is, by generating the drive signal COM by the DA conversion circuit (drive signal generation circuit 70), a plurality of types of drive signals COM (drive waveform W) can be easily generated from one waveform generation circuit 71, and the nozzle It is also possible to easily generate a drive signal COM composed of two types of drive waveforms with different periods during a period in which ink droplets are ejected once (time t0 to time t3 in FIG. 9A).

  Next, the first waveform W1 and the second waveform W2 will be described. The first waveform W1 from the time t0 to the time t2 is the “waveform for ink ejection”, and the second waveform W2 from the time t2 to the time t3 returns the volume of the contracted pressure chamber to the reference volume, and ink drops The role of aligning the potential before and after ejection (intermediate potential Vc), the vibration in the pressure chamber generated by applying the first waveform W1 (vibration due to the natural vibration period Tc, hereinafter referred to as Tc vibration), and the meniscus associated therewith It is a “damping waveform” that plays the role of suppressing vibration.

FIG. 9B is a table in which parameters of waveform equations representing the first waveform W1 and the second waveform W2 are summarized. Both the first waveform W1 and the second waveform W2 can be expressed by the following waveform expressions. Note that V (t) is the drive potential V (t) [V] at time t.
V (t) = A · exp (−γ · t) · sin (ωt + φ) + B
A [V] is the amplitude, ω [rad / S] is the angular frequency, φ [rad] is the phase adjustment amount (initial phase), and B [V] is the negative value of the minimum potential Vl. Thus, the amount of potential (amplitude center adjustment value) obtained by increasing the intermediate potential Vc is shown. That is, the first drive signal COM1 is composed of two types of sine waves (drive waveforms W1, W2) having different periods during a predetermined period (time t0 to time t3) during which one liquid droplet is ejected from the nozzle.

In Example 1, since the γ value of exp (−γ · t) is set to zero (γ = 0), the first waveform W1 and the second waveform W2 constituting the first drive signal COM1 are expressed by the following equations. It can also be expressed as
V (t) = A · sin (ωt + φ) + B

  The first waveform W1 has a larger angular frequency ω and a shorter period T (T = 2π / ω) than the second waveform W2. The first waveform W1 has a larger amplitude A than the second waveform W2. As a result, during ink discharge (application of the first waveform), the ink discharge portion (piezo element / pressure chamber) can be greatly deformed in a short period of time, and a strong pressure is generated in the pressure chamber, and the amount of ink discharged Can be increased.

  On the other hand, when the volume of the pressure chamber is returned to the reference volume after ink ejection and the Tc vibration is suppressed, the ink ejection portion is slowly deformed by the second waveform W2. This is because one head 41 has a large number of ink ejection portions (piezo elements / pressure chambers), and thus there is some variation in the manner in which Tc vibration is generated by the ink ejection portions. It is assumed that the period of the second waveform W2 is determined in accordance with the natural vibration period Tc of a certain ink ejection unit. Then, when the second waveform W2 is used for the other ink discharge portions, there is a possibility that the Tc vibrations of the other ink discharge portions may be vibrated depending on variations in the natural vibration period Tc. Therefore, the period T2 of the second waveform W2 is set to be relatively long so that the effect of damping is obtained for all the pressure chambers.

  By the way, in the trapezoidal drive signal COM ′ in FIG. 8, the timing of expanding the pressure chamber is adjusted in the potential holding period (time T3 to time T4) after ink droplet ejection, and the meniscus vibration is suppressed. On the other hand, the first drive signal COM1 of the present embodiment does not have a potential holding period, but the potential increase rate with respect to the predetermined period is smaller at a point near time t2 than at a point near time t3. Therefore, the point in the vicinity of time t2 corresponds to the potential holding period of the trapezoidal wave driving signal COM ′, and when the meniscus is largely drawn into the pressure chamber side at the point in the vicinity of time t3, Since the chamber expands greatly, the vibration of the meniscus can be suppressed.

  As described above, since the first drive signal COM1 has a plurality of types of drive waveforms (sine waves) having different periods T during one ink droplet discharge period, ink can be discharged more effectively. Vibration can be suppressed, and a drive signal according to the purpose can be used. Note that the trapezoidal drive signal COM ′ includes a high-frequency component and unintentional vibration occurs in the piezoelectric element and the pressure chamber. However, the first drive signal COM1 is unique to the pressure chamber. There is no drive waveform W having a period shorter than the vibration period Tc.

  When the drive signal COM has a plurality of types of drive waveforms with different periods T during one ink droplet ejection period, the drive waveform W can be switched by changing the DAC value output by the controller 10. For example, when the controller 10 calculates the DAC value based on the common waveform formula (V (t) = A · sin (ωt + φ) + B) of the first waveform W1 and the second waveform W2, the first waveform W1 What is necessary is just to change the parameter of a waveform type, when switching to 2 waveforms W2.

  By the way, at time t2, which is a switching point between the first waveform W1 and the second waveform W2, the drive potential V (t2) indicated by the first waveform W1 and the second waveform W2 is equal, and the first waveform W1 and the second waveform W2 are the same. Are equal to each other (the value of the first derivative of the waveform equation). In this way, at the switching point (time t2) of the drive waveform W, the drive potentials indicated by the drive waveforms before and after switching are made equal, and the slopes of the waveform equations of the drive waveforms before and after switching are made equal, so that the slopes are continuously increased. A changing potential signal is obtained, and a sudden potential change at the switching point can be prevented. As a result, since a bent portion does not occur at the switching point, it is possible to suppress the occurrence of unintended vibrations in the ink discharge portion.

  In addition, at time t2, which is a switching point between the first waveform W1 and the second waveform W2, the slopes of the first waveform W1 and the second waveform W2 are “zero”. In this way, even if a phase shift occurs when switching the drive waveform W by switching the type of the drive waveform W at a point where the slope of the drive waveform W is zero (or as small as possible), at the switching point, The error of each drive potential indicated by the drive waveforms before and after switching can be made as small as possible. However, if the drive potentials indicated by the drive waveforms before and after switching are made equal, and the slopes of the waveform equations of the drive waveforms before and after switching are made equal, the potential change becomes smooth and unintentional vibration of the ink ejection unit can be suppressed. The slope of the waveform equation of the drive waveform before and after switching need not be zero.

  Further, it is preferable that the switching point of the drive waveform W does not exist during a period in which ink is ejected from the nozzles, but exists after the ink ejection is completely completed. This is because, if the drive waveform W is switched before the ink discharge is completed and a potential error occurs, a predetermined amount of ink will not be discharged. In the case of the first drive signal COM1, since the ink ejection ends between time t1 and time t2, the first waveform W1 is switched to the second waveform W2 at time t2.

In the first waveform W1 for ink ejection, the initial phase at the time t0 is adjusted by the parameter “φ”, and the driving potential V (t0) at the time t0, that is, the intermediate potential Vc is the center of the amplitude of the first waveform W1. It is set lower than the potential. By doing so, the pressure chamber can be expanded and contracted more greatly, and as a result, a large amount of ink can be ejected. On the other hand, by shifting the initial phase “φ” of the first waveform W1 and setting the intermediate potential Vc to be relatively low, the amplitude A of the second waveform W2 becomes smaller than the amplitude A of the first waveform W1. Therefore, by adjusting the initial phase “φ”, it can be said that the intermediate potential Vc can be made uniform even for the drive signal COM having two types of drive waveforms W1, W2 having different amplitudes. As a result, the volume (reference volume) of the pressure chamber before and after the application of the drive signal COM can be made constant, and the drive signal COM can be used repeatedly.
Further, the viscosity of the ink varies depending on the environmental temperature around the head 41, and the ink viscosity is low when the environmental temperature is high, and the ink viscosity is high when the environmental temperature is low. Therefore, the parameters of the waveform equation (amplitude A and angular frequency ω) representing the drive signal COM are set according to the environmental temperature so that a predetermined amount of ink is ejected regardless of the environmental temperature change around the head 41. You may change it. For example, when the periphery of the head 41 is at a high temperature, the ink is likely to be ejected. Therefore, the amplitude A may be reduced and the angular frequency ω may be reduced.
Thus, by changing the parameter indicated by the drive signal COM, the drive signal COM according to the purpose can be applied to the piezo element.

  Further, although the drive signal for performing the fine vibration is not specifically shown, it is possible to prevent the ink from being accidentally ejected during the fine vibration by using a sine wave like the drive signal COM1. Therefore, the drive signal for fine vibration can also be expressed by the same waveform formula (V (t) = A · exp (−γ · t) · sin (ωt + φ) + B) as the first waveform W1 and the second waveform W2. For example, in the drive signal for fine vibration, the amplitude A may be made smaller than the waveform equation of the first waveform W1.

  FIG. 10 is a diagram illustrating pressure chamber pressure variation due to the first drive signal COM1 and pressure chamber pressure variation due to Tc vibration. In the drawing, the first drive signal COM1 is represented by a solid line, and the Tc vibration is represented by a dotted line (Note that since the Tc vibration may be discontinuous due to the influence of ejection, it is a thin line after time T3. ). The potential of the first drive signal COM1 increases from time T0 to time T1, and the pressure chamber expands accordingly. From time T1 to time T3, the potential of the first drive signal COM1 decreases, the pressure chamber contracts, and ink is ejected. At time T3, the first waveform W1 is switched to the second waveform W2. The period of the first waveform W1 is T1 (= T0 to T4), and the period of the second waveform W2 is T2.

  When the drive signal COM is applied to the piezo element, free vibration (vibration represented by the equivalent circuit in FIG. 7) occurs in the piezo element, the pressure chamber, and the meniscus. In particular, it can be said that free vibration (Tc vibration) in the pressure chamber greatly affects ink ejection. The natural vibration period Ta (for example, 2 μm) of the piezo element is shorter than the natural vibration period Tc (for example, 7 μm) in the pressure chamber, and conversely, the natural vibration period Tm (for example, 100 μm) of the meniscus itself is the Tc vibration. Since it is very long in comparison, it can be said that the influence on ink ejection is small.

Therefore, in Example 1, the period T1 of the first waveform W1 applied to the piezo element when ink is ejected from the nozzle is set to the natural vibration period Tc of the Tc vibration. That is, the angular frequency ω1 of the first waveform W1 is made equal to the natural angular frequency ωc of the Tc vibration. In this embodiment, the natural angular frequency ωc of the Tc vibration is 10.5 × 10 ⁵ [rad / S], and the natural vibration period Tc is 6.0 [μs]. Then, the Tc vibration generated by the expansion of the pressure chamber from time T0 to time T1 by the drive signal COM1 exerts a force in the direction of contracting the pressure chamber from time T1 to time T3. Therefore, from time T1 to time T3, the pressure chamber is contracted by the drive signal COM1, and further, the pressure chamber is contracted by Tc vibration, so that the pressure chamber is contracted with a larger force.

  That is, in the drive signal COM, the period (T1) of the drive waveform (W1) belonging to the ink droplet ejecting process (from time T0 to time T3) is made equal to the natural vibration period Tc in the pressure chamber, whereby the drive signal COM The contraction of the pressure chamber caused by Tc and the contraction of the pressure chamber caused by Tc vibration can be synchronized, and the pressure chamber can be further contracted. Further, since the first waveform W1 having a period equal to the natural vibration period Tc in the pressure chamber expands the pressure chamber, the pressure chamber can be expanded more greatly. As a result, the ejection efficiency is improved and a large amount of ink can be ejected. In other words, ink droplets can be ejected with a small potential change, leading to a reduction in power consumption.

  Since the Tc vibration is generated by the expansion of the pressure chamber by the drive signal COM, in particular, the period of the drive waveform belonging to the process of contracting the pressure chamber (time T1 to time T3) is the natural vibration period in the pressure chamber. If equal to Tc, the contraction of the pressure chamber due to the drive signal COM and the contraction of the pressure chamber due to the Tc vibration can be synchronized, and ink ejection efficiency can be increased.

<Embodiment 2: Second drive signal COM2>
FIG. 11A is a diagram illustrating the second drive signal COM2 of the second embodiment, and FIG. 11B is a table summarizing parameters of the waveform equations of the first decomposition waveform Wa1 and the second decomposition waveform Wa2. 12A is a diagram illustrating the first decomposition waveform Wa1, FIG. 12B is a diagram illustrating the second decomposition waveform Wa2, and FIG. 12C is a diagram illustrating the second drive signal COM2 and the first decomposition waveform Wa1 (first sine wave). It is the figure which showed the 2nd decomposition waveform Wa2 (2nd sine wave) on the same graph. The second drive signal COM2 of the second embodiment is a waveform obtained by adding two decomposition waveforms Wa1 and Wa2 represented by different waveform expressions (corresponding to expressions) “V (t) = A · sin (ωt + φ) + B” ( Hereinafter referred to as a synthetic wave). The second drive signal COM2, which is a composite wave, is a potential signal represented by a sine wave, and the slope continuously changes.

  As shown in FIG. 12B, the potential of the second decomposed waveform Wa2 increases from time t0 to time t1, and then continues to decrease. In the second decomposed waveform Wa2, the potential becomes a negative value after time t6. On the other hand, the first decomposition waveform Wa1 (FIG. 12A) includes a waveform of one cycle or more within one ink droplet ejection period (time t0 to time t3). Therefore, when the first decomposition waveform Wa1 is applied to the piezo element, the pressure chamber expands during the potential increase period from time t0 to time t1, and the pressure chamber contracts during the potential decrease period from time t1 to time t5 to eject ink droplets. can do. Further, the contracted pressure chamber can be expanded and returned to the reference volume in the potential rising period after time t5.

  That is, as in the case of the first decomposed waveform Wa1, ink can be ejected by one type of sinusoidal drive waveform, and any drive waveform that is represented by a sine wave and has a continuously changing inclination can be used as a comparative example. Like the trapezoidal wave drive signal COM ′ shown in FIG. 8 (FIG. 8), it is possible to prevent unintended vibrations from occurring because there is no bending point. However, as described in the first embodiment, the waveform shape differs between a drive waveform suitable for ejection and a drive waveform suitable for vibration suppression. Therefore, in the first drive signal COM1 of the first embodiment, the type of the drive waveform is switched and the waveform shape is changed at time t2 (FIG. 9), but the present invention is not limited to this, as in the case of the second drive signal COM2. Two decomposition waveforms Wa1 and Wa2 may be added.

  Next, it will be described that the drive signal COM suitable for ejection and vibration suppression is obtained by adding the first decomposition waveform Wa1 and the second decomposition waveform Wa2. For example, when a large amount of ink is desired to be ejected, the amplitude A of the ejection drive waveform may be increased to greatly expand the pressure chamber. Therefore, the first decomposition waveform Wa1 in which the potential is rising during the expansion period (time t0 to time t1) of the pressure chamber and the second decomposition waveform Wa2 in which the potential is rising during the expansion period are added. Then, as shown in FIG. 12C, the amplitude of the second drive signal COM2, which is a combined wave, becomes larger than the amplitude of each of the decomposed waveforms Wa1, Wa2, and the pressure chamber can be further expanded.

  If a large amount of ink is desired to be ejected, the potential difference between the maximum potential Vh and the minimum potential Vl may be increased to further contract the pressure chamber. Therefore, the first decomposition waveform Wa1 in which the potential decreases during the contraction period of the pressure chamber (from time t1 to time t2) and the second decomposition waveform Wa2 in which the potential has a negative value at the time t6 are added. Then, as shown in FIG. 12C, the lowest potential Vl of the second drive signal COM2 can be made lower than the lowest potential Vl1 of the first decomposition waveform Wa1.

  In other words, by setting the potential value indicated by the second decomposition waveform Wa2 to be negative from the period of contracting the pressure chamber to the period of expanding the pressure chamber, the potential decrease amount (Vh1-Vl1) of the first decomposition waveform Wa1 is reduced. The potential drop amount (Vh−Vl) of the second drive signal COM2 becomes larger, and the second drive signal COM2 can contract the pressure chamber more greatly than the first decomposition waveform Wa1. Therefore, a larger amount of ink can be ejected by using the second drive signal COM2 than the first decomposed waveform Wa1.

  In the vibration control period after ink ejection (from time t2 to time t3), the potential of the first decomposition waveform Wa1 increases while the potential of the second decomposition waveform Wa2 further decreases in the negative region. To do. Therefore, when the first decomposed waveform Wa1 and the second decomposed waveform Wa2 are combined, the potential of the second drive signal COM2 rises more slowly than the first decomposed waveform Wa1. The time at which the second drive signal COM2 reaches the intermediate potential Vc is later than the first decomposed waveform Wa1. That is, by synthesizing the first decomposed waveform Wa1 and the second decomposed waveform Wa2, the second drive signal COM2 is more controlled than the period of the drive waveform in the ink ejection process (time t0 to time t2) (time t2). From time t3) to the time t3), the period of the drive waveform becomes longer, so that even if there is variation in Tc vibrations by the ink ejection units belonging to the head 41, the vibration damping effect can be obtained for all the ink ejection units. .

  As described above, by using the second drive signal COM2 obtained by adding the first decomposition waveform Wa1 and the second decomposition waveform Wa2, more effective ejection and vibration suppression can be performed. Further, each period of the first decomposition waveform Wa1 and the second decomposition waveform Wa2 is equal to or greater than the natural vibration period Tc in the pressure chamber. The period of the second decomposition waveform Wa2 is longer than the period of the first decomposition waveform Wa1, and the second drive signal COM2 has two types of drive waveforms having different periods within one ink droplet ejection period. I can say that.

  Further, when the drive signal generation circuit 70 generates the second drive signal COM2, it is not necessary to switch the drive waveform during one ink droplet ejection period from the nozzle, so there is no possibility that a potential error occurs at the time of switching. . However, when the controller 10 calculates the DAC value based on the waveform equation (V (t) = A · sin (ωt + φ) + B) of the drive signal COM, the two waveform equations must be added to calculate the DAC value. In other words, the operation of the controller 10 is somewhat complicated.

<Embodiment 3: Third drive signal COM3>
FIG. 13A is a diagram illustrating the drive signal COM3 of the third embodiment, and FIG. 13B is a table summarizing parameters of the waveform equations of the first waveform W1 to the third waveform W3. The third drive signal COM3 is a potential signal represented by a sine wave, and the slope continuously changes. In the third embodiment, different types of drive waveforms are used in the step of expanding the pressure chamber, the step of discharging the ink by contracting the pressure chamber, and the step of damping, and the drive waveform corresponding to the purpose of each step. Is used. Therefore, the third drive signal COM3 includes a first waveform W1 for expansion (first sine wave), a second waveform W2 for contraction (second sine wave), and a third waveform W3 for vibration suppression ( (Third sine wave). The first waveform W1 to the third waveform W3 are represented by a waveform expression “V (t) = A · exp (−γ · t) · sin (ωt + φ) + B”.

The first waveform W1 has a longer period T than the second waveform W2, and as shown in FIG. 13B, the first waveform W1 has a smaller angular frequency ω than the second waveform W2. This is because if the pressure chamber is rapidly expanded in the expansion step (time t0 to time t1), air may be taken into the pressure chamber from the nozzle opening.
In the contraction process (time t1 to time t2), the second waveform W2 having a short cycle is used. Thereby, the expanding pressure chamber can be contracted at a stretch, and ink can be ejected with a stronger force. As a result, a large amount of ink is ejected. Further, the discharge efficiency is increased by making the period of the second waveform W2 equal to the natural vibration period Tc in the pressure chamber.
In the last vibration damping process (from time t2 to time t3), the third waveform W3 having the longest cycle is used. By doing so, even if there is a variation in the Tc vibration due to the ink discharge portion, the vibration damping effect can be obtained for all the ink discharge portions.
Each period from the first waveform W1 to the third waveform is equal to or greater than the natural vibration period Tc in the pressure chamber.

  As described above, the first drive signal COM1 according to the first embodiment includes the two types of drive waveforms W1 and W2. However, the first drive signal COM1 is not limited to this. It is assumed that the ink droplet ejection period may include three types of driving waveforms (sine waves) with different periods. As described in the first embodiment, it is assumed that a switching point (time t2) from the second waveform W2 to the third waveform is provided after the ink ejection is completely completed. Further, at the switching points (time t1, t2) of each driving waveform, the driving potentials indicated by the driving waveforms before and after switching are made equal. At the switching point of each drive waveform, it is preferable that the slopes of the respective waveform equations before and after the switching are made equal and the slope is as small as possible.

<Embodiment 4: Fourth drive signal COM4>
FIG. 14A is a diagram illustrating the fourth drive signal COM4 according to the fourth embodiment, and FIG. 14B is a table in which parameters of the waveform equation are summarized. In the first waveform W1 for ejection of the fourth drive signal COM4, the attenuation term exp (−γ · t) of the waveform equation “V (t) = A · exp (−γ · t) · sin (ωt + φ) + B” is obtained. Use. By doing so, the fourth drive signal COM4 has a slower rise in potential from time t0 than the first drive signal COM1 (FIG. 9). The fourth drive signal COM4 having the first waveform W1 using this attenuation term is a potential signal represented by a sine wave, and the slope continuously changes.
In this way, by slowing the rise of the potential rise, the ink ejection unit (piezo element / pressure chamber) can be started to deform without any difficulty. Further, by slowly expanding the pressure chamber, air can be prevented from entering from the nozzle surface.

Hereinafter, the reason why the rise of the potential of the drive signal becomes gentle by using the attenuation term exp (−γ · t) will be described.
FIG. 15 is a diagram illustrating a graph of the attenuation term exp (−γ · t) and the first waveform W1 ′ before correction by the attenuation term. As can be seen from the figure, the potential rising portion from time t0 of the corrected first waveform W1 is a waveform portion whose potential is lower than the center potential in the first waveform W1 ′ before correction, that is, the potential rises from the lowest potential. Corresponds to the waveform portion. However, even if an attempt is made to switch from the first waveform W1 ′ before correction to the second waveform W2, the potential difference at the switching point (time t2) is large. Therefore, if the first waveform W ′ is used without being corrected, the pressure chamber is contracted at a stretch, and unintended vibrations are generated.

Therefore, by using the attenuation term exp (−γ · t), the potential decrease amount from the time t1 to the time t2 of the first waveform W1 ′ before the correction is increased as in the first waveform W1 after the correction, and finally, At the time t2, the minimum potential Vl is reached. As a result, the drive potential when switching from the first waveform W1 to the second waveform W2 can be made equal.
Furthermore, at time t1, the first waveform W1 after correction can increase the maximum potential Vh and the pressure chamber is larger than the first waveform W ′ before correction due to the attenuation term exp (−γ · t). Can inflate. Thus, by using the attenuation term exp (−γ · t), the sine wave can be corrected to a waveform shape according to the purpose.

  Further, in the period (time t0 to time t2) during which the liquid of the fourth drive signal COM4 is ejected, the waveform portion whose potential is lower than the center potential in the first waveform W1 ′ before correction is used, so the first waveform W1 (correction). The period of the previous first waveform W1 ′) is a relatively short period. On the other hand, the period of the second waveform W2 is longer than the period of the first waveform W1 so that a damping effect can be obtained for all Tc vibrations regardless of variations in the pressure chambers. In other words, the fourth drive signal COM4 has two types of sine waves (drive waveforms W1, W2) having different periods during a predetermined period (time t0 to time t3) in which one liquid droplet is ejected from the nozzle according to the purpose. Consists of. Each period of the first waveform W1 and the second waveform W2 is equal to or greater than the natural vibration period Tc in the pressure chamber.

=== Other Embodiments ===
Each of the above embodiments has been described mainly for a printing system having an ink jet printer, but includes disclosure of a sinusoidal drive signal and the like. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About drive signal generation circuit>
In the above-described embodiment, the drive signal is generated using the drive signal generation circuit (DA conversion circuit), but the present invention is not limited to this. For example, a drive signal represented by a sine wave may be generated using an LC circuit or the like. However, since the cycle of a waveform that can be generated is fixed in the LC circuit, it is necessary to switch a plurality of LC circuits with a switch or the like in order to generate a drive signal having a drive waveform with a different cycle. Control becomes complicated.

<About the head 41>
In the above-described embodiment, the pressure chamber expands when the drive potential is increased, and the pressure chamber contracts when the drive potential is decreased, and the pressure chamber contracts when the drive potential is increased. In the case of a head in which the pressure chamber expands when the head is lowered, a drive signal obtained by inverting the drive signal shown in the figure may be used.

<About liquid ejection device>
In the above-described embodiment, the ink jet printer is exemplified as the liquid ejecting apparatus (part) for performing the liquid ejecting method, but is not limited thereto. If it is a liquid ejection device, it can be applied to various industrial devices, not a printer (printing device). For example, a textile printing device for patterning a fabric, a display manufacturing device such as a color filter manufacturing device or an organic EL display, a DNA chip manufacturing device for manufacturing a DNA chip by applying a solution in which DNA is dissolved in a chip, a circuit board manufacturing The present invention can be applied even to an apparatus or the like.
In addition, as an inkjet printer, a serial printer in which the head moves in a direction crossing the transport direction is exemplified, but the invention is not limited thereto. For example, a line head printer that completes printing by arranging nozzles in the paper width direction and conveying the paper under the nozzles arranged in a line may be used.

1 is an overall configuration block diagram of a printer according to an embodiment. 2A is a perspective view of the printer, and FIG. 2B is a cross-sectional view of the printer. 3A is a diagram illustrating a drive signal generation circuit, and FIG. 3B is a diagram illustrating generation of a potential waveform signal. It is a figure which shows a drive signal generation circuit and a head drive circuit. It is a timing chart of each signal. 6A is a cross-sectional view of the head body, and FIG. 6B is an enlarged cross-sectional view of the main part of the head body. It is an equivalent circuit of the vibration generating part of the head. It is a figure which shows the drive signal of a comparative example. FIG. 9A is a diagram illustrating the first drive signal, and FIG. 9B is a table in which parameters of the first waveform and the second waveform are summarized. It is a figure which shows the pressure fluctuation of the pressure chamber by a 1st drive signal and Tc vibration. FIG. 11A is a diagram showing the second drive signal, and FIG. 11B is a table summarizing the parameters of the first decomposition waveform and the second decomposition waveform. 12A is a first decomposition waveform, FIG. 12B is a second decomposition waveform, and FIG. 12C is a diagram illustrating a second drive signal, a first decomposition waveform, and a second decomposition waveform. FIG. 13A is a diagram showing the third drive signal, and FIG. 13B is a table summarizing parameters of the first waveform to the third waveform. FIG. 14A is a diagram showing the fourth drive signal, and FIG. 14B is a table summarizing parameters of the waveform equation. It is a figure which shows the 1st waveform before an attenuation | damping term and correction | amendment.

Explanation of symbols

1 printer,
10 controller, 11 interface unit, 12 CPU, 13 memory,
14 unit control circuit,
20 transport unit, 21 paper feed roller, 22 transport motor, 23 transport roller,
24 platen, 25 paper discharge roller,
30 Carriage unit, 31 Carriage, 32 Carriage motor,
40 head units, 41 heads, 411 case, 411a storage chamber,
412 channel unit, 412a channel forming plate, 412b elastic plate,
412c nozzle plate, 412d pressure chamber, 412e nozzle communication port,
412f common ink chamber, 412g ink supply path, 412h support frame,
412j island part, 412i elastic film, 42 head drive circuit,
42 head drive circuit, 421 first shift register, 422 second shift register,
423 latch circuit group, 424 data selector, 413 piezo element unit,
413a piezoelectric element group, 413b bonding substrate, 413c element wiring board,
50 detector groups, 51 paper detection sensors, 60 computers,
70 drive signal generation circuit, 71 waveform generation circuit, 72 current amplification circuit

Claims (14)

A potential signal generator for generating a potential signal;
A drive element that deforms when a potential signal is applied in order to eject liquid from the nozzle,
The potential signal is represented by a plurality of sine waves, and the slope continuously changes,
The potential signal applied to the drive element during a predetermined period in which one liquid droplet is ejected from the nozzle is composed of a plurality of types of sine waves with different periods.
A liquid discharge apparatus characterized by that. The liquid ejection device according to claim 1,
A pressure chamber that communicates with the nozzle and expands and contracts by deformation of the drive element;
A period of at least one of the sine waves is equal to a natural vibration period Tc in the pressure chamber;
Liquid ejection device. The liquid ejection device according to claim 2,
The liquid ejection apparatus, wherein a period of the sine wave of the potential signal applied to the driving element when liquid is ejected from the nozzle is equal to a natural vibration period Tc in the pressure chamber. The liquid ejection device according to any one of claims 1 to 3,
When the amplitude of the potential signal is A, the angular frequency of the potential signal is ω, the initial phase of the potential signal is φ, and the vibration center adjustment value of the potential signal is B, the potential signal is time t. An expression representing the drive potential V (t) that is the potential shown in FIG.
V (t) = A × sin (ωt + φ) + B
A liquid ejection device. The liquid ejection device according to any one of claims 1 to 3,
The amplitude of the potential signal is A, the attenuation term of the potential signal is exp (−γt), the angular frequency of the potential signal is ω, the initial phase of the potential signal is φ, and the oscillation center of the potential signal is When the adjustment value is B, the equation representing the drive potential V (t), which is the potential indicated by the potential signal at time t,
V (t) = A × exp (−γt) × sin (ωt + φ) + B
A liquid ejection device. The liquid ejection device according to claim 4 or 5, wherein
A pressure chamber that communicates with the nozzle and expands and contracts by deformation of the drive element;
The potential signal has a first sine wave and a second sine wave having a longer period than the first sine wave;
The first sine wave is a waveform for discharging the liquid from the nozzle by deforming the drive element and expanding and contracting a pressure chamber communicating with the nozzle by the deformation.
The second sine wave is a waveform for expanding the contracted pressure chamber and damping vibrations in the pressure chamber.
Liquid ejection device. The liquid ejection device according to claim 6,
The liquid ejection apparatus, wherein an amplitude of the first sine wave is larger than an amplitude of the second sine wave. The liquid ejection device according to claim 4 or 5, wherein
A pressure chamber that communicates with the nozzle and expands and contracts by deformation of the drive element;
The potential signal includes a first sine wave, a second sine wave having a shorter period than the first sine wave, and a third sine wave having a longer period than the first sine wave. And
The first sine wave is a waveform that deforms the drive element and expands a pressure chamber communicated with the nozzle by the deformation,
The second sine wave is a waveform for discharging the liquid from the nozzle by deforming the driving element and contracting the pressure chamber by the deformation,
The third sine wave is a waveform for expanding the contracted pressure chamber and damping vibrations in the pressure chamber.
Liquid ejection device. The liquid ejection device according to claim 8, wherein
The amplitude of the first sine wave is greater than the amplitude of the third sine wave,
The amplitude of the second sine wave is greater than the amplitude of the third sine wave;
Liquid ejection device. The liquid ejection device according to any one of claims 6 to 9,
At a point where one sine wave switches to another sine wave having a different period, the potential indicated by one sine wave is equal to the potential indicated by another sine wave,
The slope of the formula representing a certain sine wave is equal to the slope of the formula representing another sine wave,
Liquid ejection device. The liquid ejection device according to claim 10,
At the point of switching,
The liquid ejection device in which the slope of the formula representing a certain sine wave and the slope of the formula representing another sine wave are zero. The liquid ejection device according to claim 10 or 11,
The switching point is a liquid ejection apparatus that does not exist during a period in which liquid is ejected from the nozzle. The liquid ejection device according to claim 4 or 5, wherein
The liquid ejection apparatus, wherein the potential signal has a waveform obtained by adding two sine waves having different expressions. The liquid ejection device according to claim 13,
The potential signal has a first sine wave and a second sine wave having an amplitude smaller than that of the first sine wave,
The second sine wave is a liquid ejecting apparatus in which the potential value becomes negative during a period in which the pressure chamber expands from a period in which the pressure chamber communicating with the nozzle contracts.

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